# 5: Structural Determination I

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• 5.1: Prelude to Structure Determination I
William Aiken Walker was a 19th-century 'genre' painter, known for his small scenes of sharecroppers working the fields in the post-Civil War south. For much of his career, he traveled extensively, throughout the southern states but also to New York City and even as far as Cuba. He earned a decent living wherever he went by setting up shop on the sidewalk and selling his paintings to tourists, usually for a few dollars each.
• 5.2: Molecular Formulas and Empirical Formulas
Identification of unknown organic compounds often begins with the determination of the empirical and molecular formulas.
• 5.3: Mass Spectrometry
In mass spectrometry (MS), we are interested in the mass - and therefore the molecular weight - of our compound of interest, and often the mass of fragments that are produced when the molecule is caused to break apart.
• 5.4: Introduction to molecular spectroscopy
In a spectroscopy experiment, electromagnetic radiation of a specified range of wavelengths is allowed to pass through a sample containing a compound of interest. The sample molecules absorb energy from some of the wavelengths, and as a result jump from a low energy ‘ground state’ to some higher energy ‘excited state’. Other wavelengths are not absorbed by the sample molecule, so they pass on through.
• 5.5: Ultraviolet and visible spectroscopy
While interaction with infrared light causes molecules to undergo vibrational transitions, the shorter wavelength, higher energy radiation in the UV (200-400 nm) and visible (400-700 nm) range of the electromagnetic spectrum causes many organic molecules to undergo electronic transitions. What this means is that when the energy from UV or visible light is absorbed by a molecule, one of its electrons jumps from a lower energy to a higher energy molecular orbital.
• 5.6: Effect of Conjugation
• 5.7: Conjugation, Color, and the Chemistry of Vision
• 5.8: Infrared spectroscopy
Covalent bonds in organic molecules are not rigid sticks – rather, they behave more like springs. At room temperature, organic molecules are always in motion, as their bonds stretch, bend, and twist. These complex vibrations can be broken down mathematically into individual vibrational modes.

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